Loans Receivable (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfers	[1]		$ 0.0	$ 0.0	$ 0.0
Forecast changes		$ (206.5)	(46.3)	14.6	42.3
Certain Loans Acquired In Transfer Accounted For As Loans Accretable Yield Reclassifications From Nonaccretable Difference Forecast Changes, By Percentage		2.30%
Forecast Changes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes		$ (44.3)
COVID-19 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes			(162.2)
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfers	[1]		80.1	74.1	64.5
Forecast changes			(41.1)	(7.9)	2.0
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfers	[1]		80.1	74.1	64.5
Forecast changes			$ (5.2)	$ 22.5	$ 40.3

[1] Under our Portfolio Program, certain events may result in Dealers forfeiting their rights to Dealer Holdback. We transfer the Dealer’s outstanding Dealer Loan balance and related allowance for credit losses balance to Purchased Loans in the period this forfeiture occurs.